The present invention relates to material handling vehicles, interchangeably referred to herein as “lift trucks”, and more particularly, to a cyclonic motor cooling system for use in motor compartments of material handling vehicles.
Lift trucks are designed for use in various types of environments and applications. Lift trucks are configured to perform functions necessary in a given environment of use or application. Lift truck operator compartments are, in turn, designed to allow the operators to assume an operating position allowing them to perform the required material handling task.
To this end, some lift trucks operator compartments have been designed so that an operator has the option of operating the lift truck in either a standing or a seated position. Operator compartments for these types of lift trucks (e.g., a ‘sit/stand’ truck) have been modified to include, among other things, a foldable seat and an elevated footrest. Adding such a footrest, however, is difficult due to the design limitations of crowded operator compartments. One known modification for adding an elevated footrest to an operator compartment is to decrease the size of the adjacent motor compartment. This, however, comes at a cost, namely, reduced motor cooling capacity as explained below.
Standard motor compartments typically house two, and sometimes three, motors: one for propelling the forklift truck (i.e., a traction motor), one for steering (i.e., a steering motor) and one for driving a hydraulic pump to lift the fork carriage (i.e., a lift motor). These motors usually have an attached cooling fan that provides adequate cooling if housed in a standard motor compartment. When housed in a smaller motor compartment, however, the temperature therein rises at much faster rate and quickly overwhelms the capacity of the cooling fans to effectively cool the motors and other heat-generating components located therein.
To protect the motors from high temperatures, some lift trucks were outfitted with a thermal switch whereby the entire lift truck is shut down if the motor temperature is high. Other lift trucks are provided with advanced control schemes that reduce the speed and/or acceleration of overheated motors to cool them. However, both of these schemes require additional logic and circuitry and do not act to dissipate the heat once generated.
Most lift trucks are therefore provided with some sort of ventilated motor compartment. The most basic of which is a compartment with one or more openings therein to allow for the circulation of ambient air. If the motor compartment or openings are large enough, or if there is only a minimal amount of heat generated, the limited cooling capacity of such openings may suffice. However, forklifts are typically operated indoors at low speeds (and even standing still) and as a result, only minimal ventilation (and thus cooling) occurs.
Some lift trucks are provided with motor compartments having a forced-air cooling system. In such a system, hopefully cooler ambient air is directed through the motor compartment to remove an amount of heated air therefrom for conventional heat dissipation away from the compartment. In such a system, however, the forced cooling air has a generally linear air flow profile as it passes through the motor compartment. The linear flowing cooling air is impeded by the motors, reducing the amount of air flowing through the compartment and transferring heat from the motors therein. Utilizing a larger blower merely results in the greater introduction of dust and debris into the motor compartment which then accumulates on the motors and decreases the heat removal effectiveness of the forced cooling air.
To this end, FIGS. 1 and 2 illustrate an operator compartment 10 for a material handling vehicle 12 having a forced air motor cooling system 40. The operator compartment 10 is defined by an operator station 14 with an opening 16 for entering and exiting the compartment 10. Operator controls includes a steering wheel 18 and a control handle 20. The operator compartment 10 further includes a seat 24 adjacent to the control handle 20 and an elevated footrest 25 for use when the lift truck 12 is operated from a seated position. The seat 24 can be folded flat to provide additional space in the operator compartment 10 when the lift truck 12 is operated from a standing position. First and second deadman switches 21, 22 are provided in the floor 23 and footrest 25 of the operator compartment 10. As is known, one of the deadman switches 21, 22 must be actuated in order to operate the vehicle 12.
Adjacent to the operator compartment 10 are two motor compartments 26, 28. The first motor compartment 26 has two electric motors therein—a larger traction motor 30 and a smaller steering motor 32. The second motor compartment 28 houses the lift motor (not shown) and associated hydraulic circuit for lifting the fork carriage up and down and is not discussed in further detail herein. A more detailed discussion on the various components of a similar, side stance, lift truck can be found in U.S. Pat. No. 6,871,721 assigned to the present assignee, the contents of which are fully incorporated herein by reference.
The traction motor 30 is mounted to a gear box (not shown) and propels the truck 12 at a directed speed. The steering motor 32 controls the direction of travel of the lift truck 12. Both motors 30, 32, along with other electrical control components contained in the motor compartment 26 not shown, generate an appreciable amount of heat.
The motor compartment 26 is defined on the bottom by a lift truck chassis 34, on the sides by walls 36, and on to by a cover 38. A number of openings, e.g. air intake port 42 and exhaust port 44, are formed in the walls 36 of the motor compartment 26. The air intake port 42 directs cooling air from a fan or blower 46 into the compartment 26. The cooling air flows in a generally linear path, as shown by arrows 48, through the motor compartment 26, removes heat from the motors 30, 32 via convection, and is subsequently discharged through the exhaust port 44.
While the conventional forced air system 40 is an improvement over the cooling provided by ambient air ventilation, the linear flow profile of the cooling air limits the cooling capacity especially in point-to-point applications such as in the motor compartment 26. This is because the motors 30, 32, being located directly in the path of the cooling air for the greatest heat transfer, act to impede the cooling air and shield the back surfaces of the motors 30, 32 from the cooling air. The linear flow profile also contributes to the accumulation of thermally insulating dust and debris on the motors 30, 32 further limiting the heat removing capacity of the forced air system 40. A larger blower may help increase the air flow through the compartment 26, but this results in increased manufacturing and operating costs of the lift truck 12. Further, a larger blower would introduce even more dust and debris into the compartment 26 perhaps negating the effect of the larger blower.
Accordingly, a need exists for a motor cooling system that effectively and efficiently cools motors located in small enclosed spaces, such as found in a material handling vehicle with an ergonomically designed operator compartment. The present invention addresses these issues.